Fulfillment data comes from Shopify, but data is pushed there from your individual fulfillment platform/extension.
Most platforms push back things like fulfillment status (on order and item level), fulfillment location, fulfillment service/tracking info (
origin_location), and fulfillable quantity for each location.
As long as the above is being sent properly to Shopify by your fulfillment service, the Fulfillment dashboard will work properly. If you aren't getting fulfillment data in your report, contact your 3PL's support team to ensure the proper data is being sent to Shopify.